Batteries are used as power sources or as backup (emergency) power sources in a number of industries, including the telecommunications industry. In general, backup batteries for telecommunications purposes need to have long life times to be ready for infrequent emergency use. One particular use of batteries is as a backup power system for telephone offices and telephone systems. These backup battery power systems provide the energy to power equipment in the event of an electrical outage or failure.
Maintaining the reliability of battery power systems, especially backup battery power systems is extremely important. However, several problems can arise in known battery power system configurations. In particular, FIG. 1 shows a typical battery power system configuration as is known in the prior art. The configuration shown in FIG. 1 includes at least one rectifier 10, that receives AC power from a standard AC power source and that converts the AC power to DC power, DC distribution means 20, that distributes the DC power to equipment 30, such as office equipment. In a telecommunications setting, the office equipment may include converter plants, ringing plants, embedded power sources, protected AC loads and the like. A secondary distribution means 40, may be included to distribute DC power for secondary purposes, such as switches, tolls or local equipment as may be required. The rectifier 10, provides current to float and to recharge the battery array 50. The rectifier 10, maintains the battery array 50, at a constant voltage, usually 52.08 volts for flooded lead acid batteries or 54.48 volts for valve regulated lead acid batteries.
The battery power system configuration shown in FIG. 1 is typical of the highly reliable configuration used in telephone offices where flooded lead acid batteries are employed in a controlled environment. However, the same configuration has been used in remote cabinets which do not have a controlled temperature environment and which employ valve regulated lead acid (VRLA) batteries. VRLA batteries are typically used in outdoor environments because they have a higher energy density than flooded lead acid batteries and thus allow a smaller cabinet to be used.
Batteries in general, but in particular VRLA batteries that are used in an uncontrolled temperature environment, exhibit four major problems when used in the configuration shown in FIG. 1. In particular, batteries are susceptible to thermal runaway, shorted cells, short life and decreased capacity over the life of the battery. One cause of these problems is that in the configuration shown in FIG. 1 there is no means for controlling the current being provided to the batteries from the rectifiers. Thermal runaway may occur because current creates heat and heat in a turn increases the current in a continuous pattern until the current increases to a level which destroys the battery. In addition thermal runaway may occur if one or more of the battery cells shorts. In such a case, the voltage increases to the remaining good battery cells since the total voltage across the battery bank is fixed. This leads to increased temperature which as noted above increases current and may result in thermal runaway. Both thermal runaway and shorted battery cells shorten the life of the battery and reduce the capacity of the battery. Thermal runaway is a catastrophic event that can result in explosions and fires.
Therefore, there is a need in the art for a new battery power system configuration, especially for use with VRLA batteries that are deployed in an uncontrolled temperature environment that overcomes the problems associated with the prior art configuration and keeps the batteries on-line without risking loss of power to the load after an AC power failure.